The biochemical explanation for the existence of multiple liver microsomal mixed-function oxidase activities has not been obtained. There may be multiple forms of cytochrome P450 or there may be one hemoprotein and several inducable effector proteins which impart substrate specificity and spectral properties to the hemoprotein. The objective of this proposal is to distinguish between these two possibilities. Microsomal proteins have been resolved by SDS-polyacrylamide gel electrophoresis and proteins which are induced by phenobarbital and 3-methylcholanthrene have been identified. A method has been developed to identify protein bands in SDS-polyacrylamide gels. The proposal is to determine if the proteins that have been observed to be induced by phenobarbital and 3-methylcholanthrene are different cytochrome P450 molecules or if there is one cytochrome P450 and several inducable effector proteins. The method is based upon the fact that antibodies to microsomal proteins, purified after either SDS- or protease-solubilization, will precipitate detergent-solubilized enzymes. The immunoprecipitates obtained will be identified spectrally and the electrophoretic mobility of the antigen will be determined. The antibodies will be used to purify the detergent-solubilized proteins for peptide mapping.